Oscilloscope measurment error?

[Krunom]

I measure some behaviours of ferroresonant circuit and the main goal of
measurment is to
determine for which amplitude of AC voltage source i get current with
doubled frequency compared
with frequency of source.

Well, i must determine for which E of voltage source E*sin(2*pi*f*t) i get
current with frequency 2*f...

I only can detect this behaviour with looking on oscilloscop to see waveform
of current and with increasing
of E to determine the moment (and, of course, value of E) in which frequency
of current becomes 2*f...

I made this measurments but my problem is to calculate measurment error
(unrealibility?).. If i measure something
with voltmeter i have in its specifications data about its
inrealibility/error and then i can write measurment result
something like this:

measured voltage= 5V +- 10%, or
measured voltage= 5V +- 0.5V...

But how to determine this value (+-10% or +-0.5V) for oscilloscope at which
im looking and waiting to see doubled
frequency of current...?


Thanks...

P.S. It would be easier if i had "Frequencymeter" but i dont have it and
because of that i must determine wanted value E
only with Oscilloscop-display and with my eyes waiting for 2f frequency of
current...

 

[murgatroid]

That is listed in the Oscilloscope specs, and then you have to eyeball it,
so that can be 3% too.

 

[Dombo]

On Wed, 25 Aug 2004 00:14:35 +0200, Kruno Milicevic wrote:

Thanks to all for replies...

See if you have had your scope calibrated recently and
if there are accuracy specifications available for it.

Its calibrated and i have the specifications. But there is small
complication about the measurment. Ill describe shortly measurment process:
Im increasing manualy E (AC voltage source: E*sin(2Pi*f*t)) and im looking
current wave form at oscilloscope display and waiting to see that the
frequency of current equals 2*f (double source frequency) and then im
reading the value of E (at the display of some other instrument). Now should
i write result something like this:

E=10V+-0.1V.

I know that all instruments have influence on measurment error, but i want
to know what is the influence of Oscilloscope because im not using any
"numeric" values from oscilloscope, im only "looking" at display and waiting
to recognize "frequency of current" = 2*"source frequency"...

Should i simply use error-data from oscilloscope-manual or is it more
complicated because of subjective nature of measurment: "...im only
"looking" at display and waiting to recognize"... hmmm.. im waiting to
recognize... what is my "error"....? maybe is this the main question...

I hope its more clear now...

Thanks...

What is the bacndwith of the scope and at which frequency are you
measering?
Do not forget that the bandwith of a scope is specified at the -3db point.
So the amplitude error could be 30% ....

-bent